Many facilities for the storage of liquid and gaseous products such as crude and refined petroleum products, are located in terminals at the water's edge. To transfer these liquids either by a loading or offloading operation to a vessel, the terminals are normally provided with the usual docking means. The vessel or tanker can thereby be fixed in place and connected to the desired flow lines.
The vessels for transporting liquid and gaseous petroleum products are relatively large and consequently require water depths often exceeding 100 feet in which they must be maneuvered. Since many of the present terminals are at locations which do not enjoy the advantage of being accessible to deep water, these larger vessels cannot be readily used.
One method for overcoming this problem is through the use of offshore moorings which can be positioned in a water depth at which the larger vessels can be operated. Thus, the mooring is positioned sufficiently far from the loading facility to permit it to receive and hold the large vessels in place during a cargo transfer operation. This latter operation embodies the use of a plurality of conduits which extend along the ocean floor between the mooring and the onshore storage facility.
Offshore vessel mooring systems have been successfully used in many instances. However, where the terminal is located in waters which are customarily plagued by floating ice, the mooring problem is accentuated. For example, sheet ice in any body of water has the capability of building into larger floes which, over a period of time, can impair liquid transfer operations in the area. Further, the presence of sheet ice which moves through an area can exert a considerable force against anything, including a loading mooring, positioned in its path.
It can be appreciated that the presence of an offshore mooring of the type above described, if positioned in an ice infested body of water, will operate only with difficulty. Specifically it will be subjected to extreme wear and displacing forces due to the presence of moving ice along the surface of the water.
A further disadvantage experienced with the offshore loading means of the type contemplated is that the displacing forces exerted by a moored vessel can be greatly accentuated in severe weather conditions. Thus, both wind and waves acting against a vessel greatly accentuate the forces which in turn exert a displacing pull on a mooring column.
Mooring columns, staples, or masts are generally fixed in place through a pivotal joint at their lower end. The column therefore has the capability of being deflected from a normally vertical position. The lower end of the column, however, normally includes a fixed base or foundation which is piled into the ocean floor with sufficient piles to exert a desired restraining force.
In this type of mooring arrangement, however, a heavy pull or tension exerted along the water's surface by a vessel, will in turn exert a considerable force against the pivotal connection between the column and base. This connector is a vital part of the overall system. To be effective therefore it must be either strengthened, or protected to avoid being damaged by forces exerted by either ice, or a moored vessel.
Toward overcoming the above noted problems associated with offshore mooring of vessels, there is presently provided a mooring system including a mast, which is operably fixed to the ocean floor. In the normal manner, the upright mast is comprised of an elongated body connected at its lower end through a pivotal joint to a fixedly positioned foundation.
The structure and bracing of the upright mast are such that it can be deflected from a vertical position in response to the normal displacing forces which add to the pull of a moored vessel.
The upper end of the mast is provided with a relatively thin column which presents a minimal surface against which moving ice can act. Thus, the column extends from a point below the water's surface to a distance thereabove. Means is provided in the column for engaging the mooring lines of a vessel to which it is detachably engaged. It also includes fluid conducting conduits or hoses which will be communicated with the vessel's cargo tanks for an on or offloading operation.
The mooring mast is provided with a pluraliy of anchored support cables positioned thereabout. Thus, the forces normally exerted by a moored vessel will cause the mast to deflect and it will be transmitted into the support cables and remote anchors rather than into the structure of the column and its pivotal connector.
In one embodiment, the respective cables are terminated at the mooring foundation by way of a plurality of pile anchors which are embedded into the ocean floor a desired distance away from the foot of the column. Said anchors are preferably spaced radially from each other to best absorb forces exerted by the vessel and by moving ice.
It is therefore an object of the invention to provide a mooring mast or facility for a marine vessel which is capable of operating in ice infested waters to permit either an on or offloading of a fluid cargo between the vessel and a shore facility.
A further object is to provide a mooring means of the type contemplated which can be subjected to induced oscillations for the purpose of breaking up sheet ice formations which tend to solidify at the water's surface.
A still further object is to provide a cable supported mooring mast of the type contemplated which will engage a floating vessel in a manner to permit transfer of the vessel's lateral pull to a plurality of anchoring cables, rather than to the mast.